Field of the Invention
The present invention relates to a silver powder for silver clay having excellent sinterability and silver clay including the same silver powder.
Priority is claimed on Japanese Patent Application No. 2012-002339 filed on Jan. 10, 2012, the content of which is incorporated herein by reference.
Background Art
Jewelry and artistic craft objects made of silver may be manufactured by casting or forging a silver ingot. On the other hand, in recent years, silver jewelry or silver artistic craft objects are also manufactured by a method using a commercially available silver clay including a silver powder. In this method, jewelry or artistic craft objects having a desired shape are manufactured by shaping the silver clay to have the desired shape, and subsequently firing the shaped silver clay. In this method, the silver clay may be shaped to have an arbitrary shape in the similar manner as the general clay craft objects. After drying the shaped body, the shaped body is carried to the place of the firing furnace, and is fired in the furnace. By this simple method, it is possible to manufacture jewelry or artistic craft objects made of silver very easily.
Development of silver powder for silver clay having excellent sinterability has been reported in Japanese Patent No. 3687419. This silver powder has a composition containing one or two or more selected from the group consisting of Sn, Pb, Cu, Bi, and Fe in total amount of 20 to 900 ppm, and the balance consisting of Ag and unavoidable impurities.
Japanese Patent No. 3687419 has proposed production of silver clay containing 50 to 95% by weight of silver powder, 0.8 to 8% by weight of binder, 0.1 to 3% by weight of fat, 0.03 to 3% by weight of surface active agent, and a balance of water using the above-described silver clay. It is possible to achieve silver jewelry or a silver artistic craft object having a desired shape by forming this silver clay into a desired shape, drying and subsequently firing the silver clay.
As described above, a silver clay may be generally freely shaped in similar manner as a soil-clay craft object. Silver jewelry or a silver artistic craft object may be produced by drying and subsequently firing the thus achieved shaped body. There are large varieties of shapes in silver jewelry or the silver artistic craft objects, and the silver clay is shaped in accordance with the desired shape.
Silver jewelry or artistic craft objects have various shapes including a shape totally constituted of a flat or curved plate or a shape partially comprising a flat or a curved plate. The silver clay is shaped in accordance with these various shapes, dried, and subsequently fired.
For example, in some cases, jewelry is made by forming plate-shaped or a film-shaped sintered body on a substrate made of, for example, ceramics. For example, Japanese Unexamined Patent Application First Publication No. 2000-327462 describes a composition for sintering a noble metal formed by adding a binder to an inorganic powder composed of a powder of noble metal such as silver, sintering enhancing agent, and bonding enhancing agent composed of a metal compound powder or glass powder, and keening the inorganic powder added with the binder to form a clay or a slurry. Japanese Unexamined Patent Application First Publication No. 2000-327462 describes that a noble metal film with high adhesion to the ceramic shaped body can be formed by using the composition.
When the above-described shaped body of a silver clay formed into a plate shape is fired, the obtained shaped body achieves a flat surface corresponding to the desired shape. However, where the plate-shaped portion of the sintered body is thin, defective sintering such as numerous occurrence of scabs on the flat surface may occur as shown in FIG. 2. Where a large number of scabs are formed, the scabs may disturb decoration (ornament) of the silver jewelry or artistic craft object, and deteriorate the desired appearance of decoration, or may result in formation of decoration apart from the desired design.
An object of the present invention is to provide a silver clay that is capable of suppressing occurrence of scabs in a fired body formed by drying and firing a shaped body, and to provide a silver powder that can be used in such a silver clay.